Kara gains a new ally when the lightning-fast superhero The Flash (Grant Gustin) suddenly appears from an alternate universe and helps Kara battle Siobhan, aka Silver Banshee, and Livewire in exchange for her help in finding a way to return him home.

The Flash and Supergirl crossover airs Monday, March 28th at 8pm ET on CBS starring Melissa Benoist and Grant Gustin.